1. Field of the Invention
The present invention relates to a method of data placement and control in a block-divided distributed parity disk array.
2. Description of the Related Art
A redundant array of independent disks (RAID) is one of representative data storage devices. The RAID is a high performance and mass storage device that provides single virtual disk using multiple physical disks, and the RAID is a safety device that recovers data by replicating data and storing replicated data in the multiple physical disks. The RAID device has a characteristic that the performance thereof becomes decreased if the reliability of the RAID increases. In the RAID, a disk level is classified according to a method of placing data and parity information in a disk. The RAID has different characteristics according to each of the disk levels.
A RAID 0 level is used to configure a high performance mass storage device without replicating data. In this case, the reliability thereof is degraded in proportional to the number of disks.
A RAID 1 level is a method of creating an exact copy of a set of data on two or more disks. The RAID 1 level provides high performance and superior reliability, but wastes the disk space.
A RAID 5 level is a method of enabling one parity block to recover one disk error through a disk. When a lot of physical disks are managed through the RAID 5 level, the performance is lowered, the reliability is degraded, and the safety problem is arisen.
In the RAID 5 level, a strip is arranged at each disk. In order to write one block, the RAID 5 level writes a new parity block and a new data block through performing an XOR operation on related blocks. Since two write operations are performed for writing one block, the RAID 5 level is inefficient.
If the write operation is performed through delay-writing that gathers blocks composing one strip and writes the blocks of one strip, an overhead occurs for buffering the blocks. The RAID has a disk error recovering function using multiple disks. However, the RAID is inefficient to process large data or multimedia data because the RAID was developed to process on general data.